Aquatic structures, in particular immersed marine structures that come in contact with water, especially sea water, have a tendency to become fouled by marine organisms. Fouling release paint systems are abundantly used for such structures, e.g. ships, buoys, watercraft structures, etc. in order to suppress settlement of such marine organisms. Fouling-release coating systems for steel structures typically include three principal layers, namely an epoxy-based anticorrosive layer applied to the steel substrate, a fouling-release layer which typically comprises a polysiloxane-based matrix, and an intermediate layer, often referred to as a “tie-coat”, for establishing strong bonding between the otherwise incompatible epoxy-based anticorrosive layer and the polysiloxane-based fouling release layer.
U.S. Pat. No. 4,978,704 and U.S. Pat. No. 4,996,112 (Rhône Poulenc Chemie) disclose organosiloxane compositions comprising 100 parts by weight of an α,ω-dihydroxydiorganopolysiloxane polymer, 0.5-20 parts by weight of a cross-linking agent, 0.1-10 parts by weight of a bonding agent comprising an aminoorganosilicon compound having at least one amino functional group and an organosilicon compound having at least one epoxy functional group, 2-250 parts by weight of inorganic filler material, and 0.0004-3 parts by weight of a metal catalyst. The compositions are useful for the coating of marine surfaces, e.g. a ship's hull or a net.
EP 1 013 727 A1, U.S. Pat. No. 6,391,464 and U.S. Pat. No. 6,110,536 (General Electric Co.) disclose an epoxy-silicone adhesive paint as a tie-coat for a fouling-release coating. The paint comprises 80-85% by weight of an epoxy resin paint, and 15-20% by weight of a silicone adhesive promoter. The silicone adhesive promoter comprises a volatile hydrocarbon solvent, a partially condensed organosilicate, a solubilized metallic catalyst, and an aminoalkyltrialkoxy-silane.
GB 2 300 370 A1 (General Electric Co.) discloses an article having a fouling-release layer on top of an adhesion promoting layer. The adhesion promoting layer comprises an anticorrosive material (typically an epoxy-functionalized base material (e.g. an epoxy resin) combined with a curing catalyst) and a bonding agent. The bonding agent may be (i) a moisture curable grafted copolymer comprising a polydialkylsiloxane and at least one ethylenically unsaturated monomer, (ii) an aminofunctionalized polysiloxane fluid, or (iii) an α,ω-diaminofunctionalized polysiloxane fluid.
WO 99/33927 (International Coatings Ltd.) discloses a process for inhibiting fouling. The process includes the formation of a coating comprising a film-forming polymer carrying unreacted curable silicon-containing functional groups providing latent reactivity, and subsequently applying a layer comprising a curable polymeric fouling-inhibiting material and bonding the applied layer to the said coating by a condensation curing reaction involving the unreacted functional groups thereon.
JP 03-258876-A discloses a tie-coat composition comprising the reaction product of an epoxy resin and a dimethylpolysiloxane, and a hardener. The hardener should have an active hydrogen and is selected from polyamines, polyamides, aminosilane coupling agents, phenol resins, alkyd resins, melamine resins and polyurethane resins. The ratio between the epoxy equivalent number of the reaction product and the active hydrogen equivalent number of the hardener should be in the range of 100:50 to 100:200.
EP 0 521 983 discloses a primer composition comprising (A) (i) a primary amine-functional silane, or (ii) the reaction product of a primary amine-functional silane and an epoxy-functional silane, or (iii) the reaction product of a primary amine-functional silane and an α,ω-dihydroxypolydimethylsiloxane oil, (B) a chlorinated polyolefln, and (C) a room-temperature-curable polydiorganosiloxane.
In view of the above, there is still a need for improved or at least alternative tie-coat compositions for fouling-release coating systems.